It's common to see advice to "change all your passwords" following incidents like Heartbleed or Cloudbleed or after having a personal computer hacked.
This advice is useless -- it's way too time consuming, and also comes too late. If you need to change all your passwords now, you actually needed to do it six months ago.
A well-known URL that specified password requirements and an endpoint to hit with username, old and new passwords would let password managers reliably and routinely update passwords instead. To the extent "change all your passwords" is ever good advice, it would become advice you could follow automatically instead of never.
 Example of the form: https://securitywatch.pcmag.com/hacking/322494-heartbleed-fa...
This one has the benefit of being stupid simple to implement and maintain. In 10 minutes I can throw this together for all of our login stuff.
But a fully automated password changing system/API? That's not exactly as "maintenance free". Now you are maintaining a full API separate from your normal routines, and it's in an area that I always advocate for simplicity since subtle mistakes can mean compromised accounts. And the "fully automated" API would also have to work with "multi-factor" systems, which alone make everything more complicated to cover all the different ways it's done.
Don't let the possibility of a better solution kill the benefits of this simpler one.